Becoming self-employed brings freedom, but it also means you are responsible for your own tax. Unlike employees, sole traders report their income to HMRC through Self Assessment, and a missed date can quickly turn into penalties and interest.
Many new sole traders only learn about Self Assessment after a deadline has already passed. The good news is that the process is straightforward once you know the key dates and keep your records organised through the year.
In this guide we walk through the main deadlines, the penalties for missing them and the simple habits that keep your tax return stress-free.
Yes, sole traders must file a Self Assessment tax return every year, but with clear records and a simple calendar it becomes a routine task rather than a last-minute scramble.
Who Needs to File a Self Assessment Return?
You will usually need to submit a return if your self-employment income is above the trading allowance, or if you have other income that is not taxed at source. Common situations include:
– Being self-employed and earning more than £1,000 in gross trading income in a tax year
– Being a partner in a business partnership
– Receiving untaxed income, such as rental income or foreign income
If you are unsure whether you need to file, it is safer to check early. Registering late can limit your time to prepare.
Key Self Assessment Dates
The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. The main dates to remember are:
- 5 October 2026: deadline to register for Self Assessment if you are new (if you have missed it, register as soon as possible)
- 31 October 2026: deadline for paper tax returns
- 31 January 2027: deadline for online tax returns and for paying any tax owed
- 31 January 2027: first payment on account towards your 2026/27 bill, if applicable
- 31 July 2027: second payment on account, if applicable
"Most penalties are avoidable. A simple calendar, tidy records and an early start make Self Assessment far less stressful."
Penalties for Missing the Deadline
HMRC applies penalties quickly, and they build up the longer a return or payment is outstanding. At the time of writing, the main penalties include:
– A £100 fixed penalty if your return is filed even one day late
– Daily penalties of £10 per day after three months, up to a maximum of £900
– Further penalties after six and twelve months, which can be the greater of £300 or 5% of the tax due
– Interest on unpaid tax, plus additional late payment penalties at 30 days, six months and twelve months
How Riverbridge Can Help
At Riverbridge, our Personal & Business Tax service takes the pressure off Self Assessment. We prepare and file your return, explain what you owe and why, and keep you reminded of every deadline. Contact our Cardiff team for a free consultation.
This article is general information, not personal tax advice. Rates, thresholds and dates can change, so please check gov.uk or speak to an adviser about your own situation.
Looking forward to how these updates will modernize processes and strengthen the industry reputation!